When speaking to infants, adults across diverse cultures and languages use a special speech form characteristed by exaggerated intonation and other prosodic modifications. The use of infant-directed prosody appears to be a universal human parenting behavior which serves important affective and linguistic functions in early development. The long-term goal of this research project is prosody in maternal speech to the normal development of affective and linguistic communication in infancy. The central hypothesis motivating the proposed studies is that the melodies of mothers' speech to infants help the child gain access to meaning in adult speech, initially through emotion in the first year of life, and gradually through language in the second year. This project has three specific aims: 1) The first objective is to provide detailed descriptive data on the acoustic characteristics of infant-directed prosody. The first study will identify spectral and temporal characteristics of infant-directed vocalisations which contribute to their effectiveness as emotional signals. The second study will focus on acoustic cues which help the infant to identify linguistic units within the speech stream. 2) The second objective is to investigate experimentally how prosody in speech to infants elicits and communicates emotion, and modulates infants' attention. Extending our recent findings on young infants' responsiveness to vocal affect, one series of studies will investigate how adult vocalisations expressing positive and negative affect influence infants' emotion and behavior in uncertain situations. A second series of studies will investigate the hypothesis that the use of exaggerated intonation in speech to infants functions initially as an attentional device, and later as a clarification strategy, as the infant begins to acquire language, 3) The third objective is to investigate experimentally how prosodic cues facilitate speech processing and language comprehension in infants and young children. Several experiments will focus on the influence of prosodic features on infants' ability to recognize words, as well as syntactic units, in prosodic cues such as pitch and duration in speech processing. Both observational and experimental methods will be used to investigate how maternal vocalisations first become meaningful to infants through emotion and through language. The findings from this research will increase our understanding of how universal human parenting behaviors contribute to the early development of communication.